1. Field of the Invention
The instant invention relates to novel processes for the treatment of water. The invention is particularly concerned with processes for reducing the concentration of perchlorate ion from potable water sources.
2. Description of the Related Art
Perchlorate chemicals have been produced commercially in United States since the mid-1940s. Although several different perchlorate salts are manufactured, ammonium perchlorate, for example, is produced almost exclusively as an oxidizer in propellants for solid rocket motors. It is estimated that 90 percent of all perchlorate is used for this purpose. Other perchlorate salts are used in the manufacturing of explosives, fireworks and matches.
However, perchlorate production and processing methods may provide sources of groundwater pollution. Disposal of perchlorate, from manufacturing or utilization sites may occur through aqueous waste tailings, contaminated solid waste or atmospheric deposition. Deposition of these perchlorate-containing materials, usually in ponds, lakes or lagoons, or in hazardous waste landfills, provide direct pathways for groundwater contamination. For example, a primary source of perchlorate contamination is the process used to remove and recover propellant from solid rocket motors. This process consists of a high-pressure water washout of the residual propellant and generates a large quantity of ammonium perchlorate-containing wastewater, some of which enters the ground during processing by spillage. Another historic source of perchlorate contamination results from the limited xe2x80x9cshelf lifexe2x80x9d of ammonium perchlorate, necessitating frequent replacement and disposal of old stocks since the 1950""s.
Perchlorate has increasingly been found in sources of potable water. Several states have had confirmed perchlorate contamination in ground water and surface water. The concentration of perchlorate reported in wells and surface water varies widely. For example, in both northern and southern California, perchlorate was detected in 144 public water supply wells (December, 1998) with 38 of these having concentrations greater than a provisional action level of 18 ppb. The highest level of perchlorate reported in any public water supply well was 280 ppb with others greater than 100 ppb. At manufacturing facilities, perchlorate concentrations in groundwater monitoring wells were measured as high as 3.7 million ppb (US Environmental Protection Agency. xe2x80x9cPerchlorate Environmental Contamination: Toxicological Review and Risk Characterization Based on Emerging Information.xe2x80x9d (NCEA 1-0503) Washington, D.C., Office of Research and Development, 1998).
The primary health concern related to perchlorate contamination is interference with the thyroid gland""s ability to utilize iodine to produce thyroid hormones. The basis for the effect on thyroid hormone function is the competitive inhibition between iodide anion and perchlorate anion (ClO4lxe2x88x92) for thyroid gland uptake, which then results in reduced thyroid hormone production. Thyroid hormones are implicated in a number of metabolic and regulatory processes. In this regard, perchlorate causes problems for normal body metabolism, growth and development through its affect on thyroid hormone regulation.
In view of the possible negative effects towards thyroid-regulated processes, methodologies have been developed to remove perchlorate ion from drinking water. To be considered as a viable drinking water treatment technology, a process must satisfy the following criteria: (i) it must be technically capable of removing targeted pollutant(s), (ii) it must be cost-effective, (iii) it must be acceptable to the regulatory agencies and the public, (iv) it should not cause any water quality or environmental problems, and (v) it should keep waste generation to a minimum.
Ion exchange and reverse osmosis have been shown to remove perchlorate from water. Ion exchange systems, in which the perchlorate ion is replaced by an innocuous anion, e.g., chloride, has received considerable attention. These systems are capable of removing perchlorate from 20-75 ppb to nondetectable levels, such as below 4 ppb. In addition, reverse osmosis can remove between 20 and 1000 ppb of perchiorate from contaminated water with removal efficiencies upwards of 97% (Betts et al. xe2x80x9cRotating Ion-Exchange System Removes Perchlorate.xe2x80x9d Environmental Science and Technology News October (1998): 454-455). However, ion exchange and reverse osmosis processes are non-selective and remove other ions which are typically present in far higher concentrations than perchlorate, e.g., chloride, sulfate, bicarbonate. In addition, present perchlorate removal methods generate perchlorate-rich waste brines that require costly disposal.
Removal of toxins through biodegradation is expected to be one of the most cost-effective methods for removing perchlorate from drinking water. Effort has been directed at developing an anaerobic biochemical reduction processes for perchlorate ion. However, the major anticipated problem with biological processes is that biodegradation is usually too slow, especially for low level contaminants.
Another approach to remove perchlorate is by chemically treating contaminated water such that perchlorate is chemically converted to a less toxic product. However, perchlorate is known to be unreactive towards most conventional reducing agents due to slow reaction kinetics and the stability of perchlorate ion makes treatment technologies difficult, especially at low concentration levels. Further, perchlorate is a highly oxidized compound and the chemical reaction between perchlorate and commonly used reducing agents, e.g., thiosulfate, sulfite, iodide, and ferrous ion is too slow to be of practical use. Lastly, many reducing agents including titanium, vanadium, molybdenum, or ruthenium are likely to be too unstable or toxic to be used for a drinking water treatment regimen.
Accordingly, there is a need to develop new and more effective methods for removing perchlorate from water, particularly water intended for potable purposes. Methods that are efficient, safe and inexpensive are particularly desired.
It is therefore an object of the instant invention to provide new and more efficient methods for removing perchlorate ion from water by chemically treating the water, thereby converting perchlorate to a less toxic product.
It is also an object of the instant invention to provide methods for physically removing perchlorate from water that is both environmentally safe and cost effective.
In accomplishing these and other objectives, there has been provided, in accordance with one aspect of the invention, a method for chemically reducing perchlorate ion concentration in water comprising contacting water containing perchlorate ion with an effective amount of iron metal.
In a preferred embodiment, the effective amount of iron metal is about 10 g/L to about 100 g/L.
In another preferred embodiment, the step of contacting the water with iron metal is performed in the presence of a catalyst, wherein the catalyst is preferably UV light.
In yet another preferred embodiment, the step of contacting the water with iron metal is performed under substantially anoxic conditions.
In still yet another preferred embodiment, the step of contacting the water with iron metal is performed at a pH of about 6 to 8.
In yet another embodiment, the iron metal is in a powdered form or the iron metal is contained within a packed bed.
There is also provided, in accordance with another aspect of the invention, a method for removing perchlorate ion from water comprising contacting the water containing perchlorate ion with iron metal or metal oxide in the presence of phosphoric acid under conditions suitable for perchlorate to adsorb to the iron metal or metal oxide and the removing the iron metal or metal oxide with perchlorate ion bound thereto from the water.
In a preferred embodiment, the iron metal or metal oxide is present at a concentration of about 10 g/L to about 100 g/L.
In another preferred embodiment, the iron meal is an iron oxide.
In yet another preferred embodiment, the iron oxide is FeOOH.
In still yet another preferred embodiment, step of contacting the water containing perchlorate ion with iron metal or metal oxide is performed at under acidic conditions.
In again yet another preferred embodiment, the phosphoric acid is in stoichiometric excess with respect to the perchlorate ion, and even more preferably, the ratio of phosphoric acid to perchlorate ion is between about 1:1 to about 70:1.
There is also provided, in accordance with still yet another aspect of the invention, a method for removing perchlorate ion from water, comprising contacting water containing perchlorate ion with phosphoric acid under conditions suitable to form a perchlorate ion-phorphoric acid complex, passing the water through a column packed with iron metal or metal oxide, wherein the iron metal or metal oxide is immobilized within the column and wherein passing the water through the column brings the water into contact with the iron metal or metal oxide such that formed perchlorate ion-phorphoric acid complex adsorbs to the iron metal or metal oxide, and collecting the water after it passes through the column.
Other features and advantages of the present invention will become apparent from the following detailed description. It should be understood however that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from the following detailed description.